This invention relates to a dielectric material and a process for producing the same. More particularly, it relates to a dielectric material having excellent dielectric characteristics, such as a relatively high specific dielectric constant (hereinafter represented by xcex5r) in a high frequency region, a small absolute value of a temperature coefficient (hereinafter represented by xcfx84f) of resonance frequency (hereinafter represented by f0), and a large unloaded quality value (hereinafter represented by Qu), and a process for producing the same. The dielectric material of the invention is particularly useful as a resonator and a filter for a high frequency region, a matching element for various microwave circuits, and the like.
With the recent increase of communication information, various communication systems using the microwave region, such as mobile telecommunication systems, satellite communication systems, positioning systems using communication data, and satellite broadcasting, have been advancing rapidly. Many dielectric materials for microwave have been developed accordingly. The dielectric materials for microwave are required to have (1) a high specific dielectric constant xcex5r, (2) a small absolute value of a temperature coefficient xcfx84f of resonance frequency f0 (i.e., small temperature dependence of f0), and (3) a large unloaded Q-value Qu (i.e., small dielectric loss 1/Qu).
Known dielectric materials with a small dielectric loss, i.e., with a large Qu, include Ba (Mg1/3Ta2/3) O3 and Ba (Zn1/3Ta2/3) O3, and known dielectric materials with a high xcex5r include BaOxe2x80x94RE2O3xe2x80x94TiO2-based ceramics (wherein RE represents a rare earth element)
JP-A-6-275126 discloses a dielectric ceramic composition comprising Ba, Bi, Ti and O as essential components and Nd and Sm as optional components. JP-A-6-309926 and JP-A-6-325620 teach addition of an alkali metal, e.g., Na, Kor Li, to the above-described ceramic composition to further improve the dielectric characteristics, explaining that Qu, can be improved without changing xcex5r. On the other hand, it is mentioned that an increase in Bi content increases xcex5r and decreases the absolute value of xcfx84f but diminishes Qu. In fact, the ceramic compositions disclosed in the above publications have a considerable Bi content and cannot be necessarily said to have a high Qu,. Besides, the xcfx84f varies widely among the compositions.
An object of the present invention is to provide a dielectric material having a high xcex5r a small absolute value of xcfx84f, or with the xcfx84f adjusted to the negative side, and a large Qu and a process for producing the same.
Another object of the invention is to provide a dielectric material that meets the demands for communication equipment having reduced size and height and is also applicable to new uses in, for example, a duplexer while exhibiting improved dielectric characteristics and a process for producing the same. A Qu is a relatively important characteristic for use in a duplexer, etc., and it is required that Quxc3x97f0 be 5000 GHz or more, particularly 6000 GHz or more. The present invention provides a dielectric material satisfying this requirement.